The present invention relates to fuel supply systems and more particularly to multi-fuel tank systems incorporating a selector valve such as employed in airplanes and the like.
There are many instances where a liquid fuel operated engine is supplied fuel from a plurality of tanks on a selective basis by means of a selector valve interconnecting the fuel line to the engine to the selected liquid fuel tank. Sometimes, this takes place where one or more additional tanks have been added to a basic vehicle such as with recreational vehicles or the like wherein the touring range of the original fuel tank supplied with the vehicle is inadequate for desired operation.
A principal use of such apparatus is in aircraft wherein a plurality of fuel tanks are incorporated on a space-available basis within various points of the wings and/or fuselage. Such an arrangement is shown in FIG. 1. For example, one fuel tank 10 is located within the left wing and a second fuel tank 12 is located within the right wing. The output lines 14 and 16, respectively, from the tanks 10, 12 are connected as inputs to selectable positions of a selector valve 18. The output of selector valve 18 is connected through fuel line 20 to the engine (not shown). By turning the selector valve 18 to connect the left fuel tank 10, fuel flows only from left tank 10, through selector valve 18 to fuel line 20 and thence to the engine. Typically, the two fuel tanks 10, 12 are provided with fuel gauges. These gauges, however, are only an approximation and, typically, the pilot is suddenly faced with a "dead" engine when running his tanks to a completely empty condition. The selector valve 18 is then moved to the opposite tank whereupon the engine must be restarted in flight. A similar situation exists in land vehicles such as recreational vehicles as previously described. In either case, the stoppage of the engine is, normally, not disastrous. That is, it can be restarted once again. Often, however, the engine stoppage is at a time of inconvenience. For passengers, sudden stoppage of the engine in an airplane can be a frightening experience. With fuel-injected engines, the engine restart procedure can sometimes be more difficult giving even the pilot who anticipated an engine stoppage a moment of concern until the engine, in fact, restarts.
Wherefore, it is the object of the present invention to provide a method and apparatus for operation of multi-tank selectable fuel systems for supplying liquid fuel to an engine whereby individual tanks can be completely emptied but wherein sufficient operating time is supplied to the engine from a temporary source to maintain the engine in operation during the period of changeover to the next major fuel supply.